Pneumatic tires

ABSTRACT

As a tread rubber of a pneumatic tire is used a rubber composition comprising 10-150 parts by weight of a silica filler, 0-150 parts by weight of carbon black and 0.2-10 parts by weight of at least one specified silane coupling agent, based on 100 parts by weight of a particular polymer rubber having a glass transition temperature of not lower than -50° C. through polymerization of 1,3-butadiene or copolymerization of 1,3-butadiene and styrene with an organic alkali metal initiator, or a rubber blend of not less than 30 parts by weight of the above polymer and not more than 70 parts by weight of the other diene series rubber.

This is a divisional of application Ser. No. 08/100,339, filed Aug. 2,1993, now U.S. Pat. No. 5,409,967, which is a continuation ofapplication Ser. No. 07/660,812, filed Feb. 26, 1991, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to pneumatic tires, and more particularly to apneumatic tire simultaneously satisfying good wet-skid resistance,rolling resistance and wear resistance.

2. Related Art Statement

Recently, the study for reducing the rolling resistance of the tirebecome important for saving the fuel consumption in automobiles inaccordance with social demand for saving energy and resources. Ingeneral, it is known that as the rolling resistance of the tire isreduced, the fuel consumption in the automobile is mitigated to providea low fuel consumption tire. In order to reduce the rolling resistanceof the tire, generally a material having a small hysteresis loss as atread rubber for the tire can be used. On the other hand, the use of arubber material having a large friction resistance (wet-skid resistance)on wet road surface is strongly desired from the viewpoint of the demandfor the running stability. However, the low rolling resistance and thehigh friction resistance on wet road surface are conflicting with eachother, so that it is very difficult to simultaneously satisfy theseproperties.

Notably, the viscoelastic properties in the rubber composition aretheoretically related to the wet-skid resistance and rolling resistanceof the tire. That is, it is indicated to effectively reduce the fuelconsumption by decreasing the hysteresis loss of the tread rubber forreducing the rolling resistance during the running of the tire, i.e. byviscoelastically decreasing the loss factor (tan δ) at a temperature of50°-70° C. used in the running of the tire. On the other hand, it isknown that the wet-skid resistance is well interrelated to the lossfactor (tan δ) at about 0° C. at a frequency of 10-20 Hz. Therefore, itis required to make the loss factor at about 0° C. large in order toimprove the gripping performance of the tire.

As a method of decreasing the hysteresis loss, generally a materialhaving a low glass transition temperature can be used such as high-cispolybutadiene rubber and the like, or a material having a high reboundresilience such as natural rubber and the like. However, the use ofthese rubbers lowers the wet-skid resistance, so that it is considerablydifficult to simultaneously establish the running stability and the lowrolling resistance.

However, many techniques utilizing anion polymerization have beenproposed in order to solve the aforementioned problems. For example,Japanese Patent laid open No. 55-12133 and No. 56-127650 disclose thathigh vinyl content polybutadiene rubber is effective for solving theproblems, and Japanese Patent laid open No. 57-55204 and No. 57-73030disclose that high vinyl content styrene-butadiene copolymer rubber iseffective for solving the problems. Furthermore, Japanese Patent laidopen No. 59-117514, No. 61-103902, No. 61-14214 and No. 61-141741disclose that the heat generation is reduced by using a modified polymerobtained by introducing a functional group such as benzophenone,isocyanate or the like into a molecular chain of the polymer. Even inthese techniques, the low value recently required for the rollingresistance is not yet sufficient.

SUMMARY OF THE INVENTION

It is, therefore, an object of the invention to overcome theaforementioned problems of the conventional techniques and to provide apneumatic tire simultaneously satisfying good wet-skid resistance,rolling resistance and wear resistance.

The inventors have made various studies in order to solve the aboveproblems and found that the above properties of the tire areconsiderably improved by using as a tread a rubber composition obtainedby compounding silica and a silane coupling agent with polybutadiene orstyrene-butadiene copolymer rubber having a particular glass transitiontemperature (Tg) through polymerization with an organic alkali metalinitiator, preferably polybutadiene or styrene-butadiene copolymermodified with a silane compound, and as a result the invention has beenaccomplished.

According to the invention, there is the provision of a pneumatic tirecomprising a tread made from a rubber composition comprising 10-150parts by weight of a silica filler, 0-150 parts by weight of carbonblack and 0.2-10 parts by weight of at least one silane coupling agentrepresented by the following general formula:

    Y.sub.3 --Si--C.sub.n H.sub.2n A                           (I)

[wherein Y is an alkyl group or alkoxyl group having a carbon number of1-4 or a chlorine atom, provided that the three Ys are the same ordifferent, n is an integer of 1-6, and A is --S_(m) C_(n) H_(2n) Si--Y₃group, --X group or SmZ group wherein X is a nitroso group, a mercaptogroup, an amino group, an epoxy group, a vinyl group, an imido group ora chlorine atom, Z is ##STR1## group, each of m and n is an integer of1-6 and Y is the same as mentioned above)], based on 100 parts by weightof a polymer rubber having a glass transition temperature of not lowerthan -50° C. through polymerization of 1,3-butadiene or copolymerizationof 1,3-butadiene and styrene with an organic alkali metal initiator, ora rubber blend of not less than 30 parts by weight of the above polymerand not more than 70 parts by weight of the other diene series rubber.

In a preferable embodiment of the invention, the polymer is asilane-modified polymer having a glass transition temperature of notlower than -50° C. and obtained by reacting an active terminal of aresulting living polymer through polymerization of 1,3-butadiene orcopolymerization of 1,3-butadiene and styrene with an organic alkalimetal initiator with a silane compound represented by the followinggeneral formula:

    U.sub.i Si(OR).sub.j R'.sub.4-i-j                          (II)

(wherein U is a halogen atom selected from chlorine, bromine and iodine,each of R and R' is an alkyl group, an aryl group, a vinyl group or ahalogenated alkyl group each having a carbon number of 1-20, j is aninteger of 1-4, i is an integer of 0-2 and a sum of i and j is 2-4).

DESCRIPTION OF THE PREFERERD EMBODIMENTS

The polymer used in the invention can be produced by the well-knownmethod using an organic alkali metal initiator. The production of such apolymer is usually carried out in an inert organic solvent. As the inertorganic solvent, use may be made of pentane, hexane, cyclohexane,heptane, benzene, xylene, toluene, tetrahydrofuran, diethyl ether andthe like.

At first, the polymerization of 1,3-butadiene or copolymerization of1,3-butadiene and styrene is carried out in the presence of an organicalkali metal initiator. As the organic alkali metal initiator, mentionmay be made of alkyllithiums such as n-butyllithium, sec-butyllithium,t-butyllithium, 1,4-dilithium butane, reaction product of butyllithiumand divinylbenzene and the like; alkylene dilithium, phenyl lithium,stilbene dilithium, diisopropenylbenzene dilithium, sodium naphthalene,lithium naphthalene etc.

In case of the copolymerization, a Lewis base may be used as arandomizing agent and a regulating agent for microstructure of butadieneunit in the copolymer, if necessary. As the Lewis base, mention may bemade of ethers and tertiary amines such as dimethoxybenzene,tetrahydrofuran, dimethoxy ethane, diethylene glycol dibutyl ether,diethylene glycol dimethyl ether, triethylamine, pyridine, N-methylmorpholine, N,N,N', N'-tetramethyl ethylenediamine,1,2-dipiperidinoethane and the like.

Moreover, the content of bound styrene in the copolymer can becontrolled by varying the amount of styrene monomer in the monomermixture, while the introduction of styrene single chain in thecopolymer, i.e. arrangement of styrene chain without sequence of styrenechain unit can be controlled by the use of an organic potassium compoundsuch as potassium dodecylbenzene sulfonate or the like. In addition, thecontent of 1,2-bond in butadiene unit of the copolymer molecule can becontrolled by varying the polymerization temperature.

Furthermore, the living polymer may be produced by charging themonomers, i.e. 1,3-butadiene or 1,3-butadiene and styrene, the inertorganic solvent, the organic alkali metal initiator and, if necessary,the Lewis base into a reaction vessel purged with nitrogen gas at once,discontinuously or continuously.

The polymerization temperature is usually -120° C. to +150° C.,preferably -80° C. to +120° C., and the polymerization time is usually 5minutes to 24 hours, preferably 10 minutes to 10 hours.

The polymerization temperature may be held at a constant value withinthe above range or may be raised or be adiabatic. And also, thepolymerization reaction may be carried out by batch system or continuoussystem.

Moreover, the concentration of the monomer in the solvent is usually5-50% by weight, preferably 0-35% by weight.

In the formation of the living polymer, it is necessary to prevent theincorporation of a compound exhibiting a deactivation function such ashalogen compound, oxygen, water, carbon dioxide gas or the like into thepolymerization system as far as possible in order to avoid thedeactivation of the organic alkali metal initiator and the resultingliving polymer.

The silane-modified polymer used in the invention is a modified rubberpolymer having Si--O--R bond (R is the same as mentioned above) obtainedby reacting the aforementioned silane compound with an active terminalof the resulting living polymer.

The silane compound to be reacted with the living polymer is a silanecompound having at least one alkoxy group in one molecule and isrepresented by the general formula (II):

    U.sub.i Si(OR).sub.j R'.sub.4-i-j                          (II)

(wherein U, R, R', i and j are the same as mentioned above).

As the silane compound, there are preferable compounds in which OR groupis non-hydrolytic, i.e. OR is a non-hydrolytic alkoxy group, aryloxygroup or cycloalkoxy group having a carbon number of 4-20. Preferably, Rin the OR group is a hydrocarbon residue in which three carbon atoms arebonded to carbon in α-position, a hydrocarbon residue in which ahydrocarbon group having a carbon number of not less than 1 is bonded tocarbon in β-position, or an aromatic hydrocarbon residue such as aphenyl group or a toluyl group.

The term "non-hydrolysis" used herein means that when 60g of a rubbersheet shaped through hot rolls of 120° C. at a roll gap of 0.5 mm isplaced in a stainless steel vessel of 10 liter capacity together with 3liters of warm water and left to stand while boiling the warm water byblowing steam and then dried, the rise of Mooney viscosity (MLi+4, 100°C.) of the polymer is substantially not more than 10 point, preferablynot more than 5 point as compared with the non-treated polymer.

In R' of the formula (II), the alkyl group includes methyl group, ethylgroup, n-propyl group, t-butyl group and the like, and the aryl groupincludes phenyl group, toluyl group, naphthyl group and the like, andthe halogenated alkyl group includes chloromethyl group, bromomethylgroup, iodomethyl group, chloroethyl group and the like.

For example, a compound of the formula (II) in which i is 0 and j is 2is dialkyldialkoxy silane, and a compound in which i is 0 and j is 3 ismonoalkyltrialkoxy silane, and a compound in which i is 0 and j is 4 istetraalkoxy silane, and a compound in which i is 1 and j is 1 ismonohalogenated dialkylmonoalkoxy silane, and a compound in which i is 1and j is 2 is monohalogenated monoalkyldialkoxy silane, a compound inwhich i is 1 and j is 3 is monohalogenated trialkoxy silane, and acompound in which i is 2 and j is 1 is dihalogenated monoalkylmonoalkoxysilane, and a compound in which i is 2 and j is 2 dihalogenated dialkoxysilane. All of these compounds have a reactivity with the activeterminal of the living polymer.

Particularly, monoalkyltriaryloxy silane where i=0 and j=3 andtetraaryloxy silane of i=0 and j=4 are preferable because polymershaving an improved processability and a high compatibility with silicaare obtained by coupling the living polymer with such a compound.

Among the silane compounds of the formula (II) used in the invention,the alkoxy type compound containing no halogen includestetrakis(2-ethylhexyloxy) silane, tetraphenoxy silane,methyltris(2-ethylhexyloxy) silane, ethyltris(2-ethylhexyloxy) silane,ethyltrisphenoxy silane, vinyltris(2-ethylhexyloxy) silane,ethyltriphenoxy silane, vinyltris(2-ethylhexyloxy) silane,vinyltriphenoxy silane, methylvinylbis(2-ethylhexyloxy) silane,ethylvinylbiphenoxy silane, monomethyltriphenoxy silane,dimethyldiphenoxy silane, monoethyltriphenoxy silane, diethyldiphenoxysilane, phenyltriphenoxy silane, diphenyldiphenoxy silane and the like.The aryl type compound containing no halogen includes tetraphenoxysilane, ethyltriphenoxy silane, vinyltriphenoxy silane,dimethyldiphenoxy silane, monoethyltriphenoxy silane, diethyldiphenoxysilane, phenyltriphenoxy silane, diphenyldiphenoxy silane and the like.The compound containing a halogen and having a non-hydrolytic OR groupwith a carbon number of 4 includes tri-t-butoxymonochloro silane,dichloro-di-t-butoxy silane, di-t-butoxy-diiodo silane, and the like,and the compound containing a halogen and having a non-hydrolytic ORgroup with a carbon number of 5 includes triphenoxymonochloro silane,monochloromethyldiphenoxy silane, monochloromethylbis(2-ethylhexyloxy)silane, monobromoethyldiphenoxy silane, monobromovinyldiphenoxy silane,monobromoisopropenylbis(2-ethylhexyloxy) silane, ditolyloxydichlorosilane, diphenoxydiiodo silane, methyltris(2-methylbutoxy) silane,vinyltris(2-methylbutoxy) silane, monochloromethylbis(2-methylbutoxy)silane, vinyltris(3-methylbutoxy) silane, tetrakis(2-ethylhexyloxy)silane, tetraphenoxy silane, methyltris(2-ethylhexyloxy) silane,ethyltris(2-ethylhexyloxy) silane, ethyltriphenoxy silane,vinyltris(2-ethylhexyloxy) silane, vinyltriophenoxy silane,methylvinylbis(2-ethylhexyloxy) silane, ethylvinyldiphenoxy silane andthe like. The halogen-containing aryloxy type compound includestriphenoxymonochloro silane, monochloromethyldiphenoxy silane,monobromoethyldiphenoxy silane, monobromovinyldiphenoxy silane,ditolyldichloro silane, diphenoxydiiodo silane and the like.

Among these silane compounds, silane compounds in which i is 0 or 1,particularly tetraphenoxy silane and monomethyltriphenoxy silane arepreferable. These silane compounds may be used alone or in admixture.

The silane-modified polymer according to the invention is obtained byreacting the active terminal of the above living polymer with the silanecompound of the formula (II). In this case, the amount of the silanecompound used is not less than 0.7 molecule per one active terminal ofthe living polymer, preferably 0.7-5.0, more particularly 0.7-2.0. Whenthe amount of the silane compound used is less than 0.7-molecule per oneactive terminal of the living polymer, the production of branchedpolymer becomes larger and the change of the molecular weightdistribution is large and hence the control of the molecular weight andthe molecular weight distribution is difficult, while when it exceeds5.0 molecule per one active terminal of the living polymer, the effectof improving the wear resistance and fracture properties is saturatedand it becomes unfavorable in view of economical reasons.

In the production of the silane-modified polymer, two-stage addition maybe used wherein a small amount of the silane compound is first added tothe active terminal of the living polymer to form a polymer having abranched structure and then another silane compound is added to theremaining active terminal.

The reaction between the active terminal of the living polymer and thefunctional group of the silane compound is carried out by adding thesilane compound to the solution in the living polymer system, or byadding the solution of the living polymer to an organic solvent solutioncontaining the silane compound.

The reaction temperature is -120° C. to +150° C., preferably -80° C. to+120° C., and the reaction time is 1 minute to 5 hours, preferably 5minutes to 2 hours.

After the completion of the reaction, the silane-modified polymer can beobtained by blowing steam into the polymer solution to remove thesolvent or adding a poor solvent such as methanol or the like tosolidify the resulting silane-modified polymer and then drying throughhot rolls or under a reduced pressure. Alternatively, the solvent maydirectly be removed from the polymer solution under a reduced pressureto obtain a silane-modified polymer.

Although the molecular weight of the silane-modified polymer can bevaried over a wide range, the Mooney viscosity (MLi+4, 100° C.) ispreferable to be within a range of 10-150. When the Mooney viscosity isless than 10, the wear resistance is poor, while when it exceeds 150,the processability is poor.

Moreover, the structure of the silane-modified polymer used in theinvention can be confirmed, for example, by an infrared absorptionspectrum that Si--O--C bond is assigned to about 1100cm⁻¹, Si--O--o bondis assigned to about 1250cm⁻¹ and Si--C bond is assigned to about1160cm⁻¹.

The polymer or silane-modified polymer used in the invention isnecessary to have a glass transition temperature (Tg) of not lower than-50° C., preferably not lower than -40° C. When Tg is lower than -50°C., the wet-skid resistance is poor.

In the styrene-butadiene copolymer according to the invention, thecontent of bound styrene is preferable to be 15-50% by weight.Furthermore, it is favorable that the styrene single chain in thearrangement of bound styrene units is less than 40% by weight of totalbound styrene and the styrene long chain consisting 8 or more styreneunits is not more than 10% by weight of the total bound styrene. Thestyrene chain distribution according to the invention is determined bydecomposing the polymer sample through ozone and analyzing through gelpermeation chromatography (Tanaka et al., Kabunshi Gakkai Yokoshu, 29,(9), page 2055).

According to the invention, the polymer or the silane-modified polymercan be used alone as a rubber ingredient. If necessary, it may be usedas a rubber blend with not more than 70 parts by weight, preferably notmore than 50 parts by weight of at least one other diene series rubbersuch as natural rubber, cis-1,4-polyisoprene, emulsion-polymerizedstyrene-butadiene copolymer, solution-polymerized styrene-butadienecopolymer, low cis-1,4-polybutadiene, high cis-1,4-polybutadiene,ethylene-propylene-diene terpolymer, chloroprene, halogenated butylrubber and butadieneacrylonitrile copolymer rubber based on 100 parts byweight of total rubber ingredient. When the silane-modified polymer isused as a rubber blend, the amount of the silane-modified polymer usedis preferably not less than 10% by weight, preferably not less than 20%by weight per the total rubber ingredient. When the amount is less than10% by weight, the improving effect against silica is not recognized.

In the rubber composition according to the invention, the amount of thesilica filler to be compounded is 10-150 parts by weight, preferably15-100 parts by weight based on 100 parts by weight of total rubberingredient. When the amount is less than 10 parts by weight, thereinforcing effect is small and the wear resistance is poor, while whenit exceeds 50 parts by weight, the processability and the fractureproperties are poor.

Moreover, 0-100 parts by weight of carbon black may be used togetherwith the silica filler as a filler, whereby the processability, wearresistance and cut resistance can further be improved as compared withthe use of the silica filler alone. In this case, the weight ratio ofcarbon black to silica filler is within a range of 95/5-10/90 from aviewpoint of the balance of wet-skid resistance, rolling resistance andwear resistance.

As the silane coupling agent used in the invention and represented bythe formula (I), mention may be made of bis(3-triethoxysilylpropyl)tetrasulfide, bis(2-triethoxysilylethyl) tetrasulfide,bis(3-trimethoxysilylpropyl) tetrasulfide, bis(2-trimethoxysilylethyl)tetrasulfide, 3-mercaptopropyl trimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyl trimethoxysilane, 2-mercaptoethyltriethoxysilane, 3-nitropropyl trimethoxysilane,3-nitropropyltriethoxysilane, 3-chloropropyltrimethoxysilane,3-chloropropyl triethoxysilane, 2-chloroethyl trimethoxysilane,2-chloroethyl triethoxysilane,3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide,3-triethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide,2-triethoxysilyl-N,N-dimethylthiocarbamoyl tetrasulfide,3-trimethoxysilylpropyl benzothiazole tetrasulfide,3-triethoxysilylpropyl benzothiazole tetrasulfide,3-triethoxysilylpropyl methacrylate monosulfide, 3-trimethoxysilylpropylmethacrylate monosulfide and the like. Among them,bis(3-triethoxysilylpropyl) tetrasulfide, 3-trimethoxysilylpropylbenzothiazole tetrasulfide and the like are preferable. As the compoundof the formula (I) in which three Ys are different, mention may be madeof bis(3-diethoxymethylsilylpropyl) tetrasulfide, 3-mercaptopropyldimethoxymethylsilane, 3-nitropropyl dimethoxymethylsilane,3-chloropropyl dimethoxymethylsilane,dimethoxymethylsilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide,dimethoxymethylsilylpropyl benzothiazole tetrasulfide and the like.

The amount of the silane coupling agent added is varied in accordancewith the amount of silica filler added, but is is 0.2-10 parts byweight, preferably 0.5-5 parts by weight. When the amount of the silanecoupling agent is less than 0.2 part by weight, the coupling effect isvery small and the effect of improving the rolling resistance and wearresistance is not observed, while when it exceeds 10 parts by weight,the reinforcing effect lowers and the wear resistance and cut resistanceare degraded.

Moreover, the rubber composition according to the invention may befurther compounded with a powdery filler such as magnesium carbonate,calcium carbonate, clay or the like, a fibrous filler such as glassfiber, whisker or the like, zinc white, an antioxidant, a vulcanizationaccelerator, a vulcanizing agent and so on, if necessary.

The following examples are given in illustration of the invention andare not intended as limitations thereof.

In these examples, the measurements were made by the following methods,respectively.

The Mooney viscosity was measured at a temperature of 100° C. after thepreheating for 1 minute and the heating for 4 minutes.

The microstructure in butadiene portion was measured by an infraredabsorption spectrometry (Molero's method).

The content of bound styrene was measured by using a calibration curveof phenyl group of 699cm⁻¹ previously determined through an infraredabsorption spectrometry.

The properties of vulcanizate were measured according to a method of JISK6301.

A Lambourn abrasion index was measured by a Lambourn abrasion testingmethod. The measuring conditions were a load of 4.5 kg, a surface speedof grindstone of 100 m/sec, a speed of sample of 130 m/sec, a slippingrate of 305, a falling rate of stone of 20 g/min and room temperature.

The internal loss (tan δ) was measured by means of a mechanicalspectrometer made by Rheometrix Inc. at various temperatures underdynamic shearing strain having an amplitude of 1.0% and a frequency of15 Hz.

The rolling resistance index was measured by rotating the tire on a drumof 1.7 m in outer diameter to raise the rotating speed up to a givenvalue, stopping the rotation to move the drum by inertia force andevaluating according to the following equation from a calculated valuebased on inertia moment (the larger the value, the smaller the rollingresistance).

inertia moment of control tire/inertia moment of test tire×100

The skid resistance on wet road surface (wet-skid resistance) wasevaluated according to the following equation from a running distanceafter the the vehicle was subjected to a rapid braking at a speed of 80km/hr on a wet concrete road surface having a water depth of 3mm (thelarger the value, the better the wet-skid resistance).

running distance of control tire/running distance of test tire×100

The wear resistance index was evaluated according to the followingequation from average value when the remaining groove depth was measuredat 10 positions after the tire was actually run over a distance of 40000km(the larger the value, the better the wear resistance).

remaining groove depth of test tire/remaining groove depth of controltire×100

The steering stability was evaluated according to a method of ASTMF516-77.

The production of the copolymer to be used in the tread of the test tirewill be described below.

Production Example 1

Into a reaction vessel of 50 l capacity 25 kg of cyclohexane, 1.4 kg ofstyrene, 4.5 k g of 1,3-butadiene, 2.6 g of n-butyllithium, 0.5 g ofsodium dodecylbenzene sulfonate and 1.8 g of ethylene glycol dimethylether were charged, which was polymerized in a nitrogen atmosphere at apolymerization temperature of 45° C. for 1.5 hours. After the remaininginitiator was removed, the resulting polymer was dried to obtain astyrene-butadiene copolymer (copolymer No. 4 in Table 1).

Various copolymers shown in Table 1 were obtained by varying thecharging ratio of styrene the polymerization temperature, the amount ofsodium dodecylbenzene sulfonate and the like.

                                      TABLE 1    __________________________________________________________________________    Copolymer No.    1  2  3  4  5  6  7  8    __________________________________________________________________________    Content of bound styrene (wt %)                     5  25 10 25 40 40 41 55    Content of 1,2-bond (wt %)                     65 15 72 50 22 21 23 20    Styrene single chain of styrene                     85 37 77 68 49 33 36 34    unit (wt %)    Styrene long chain f 8 or more                     0  2  1  1  6  2  15 5    styrene units (wt %)    Glass transition temperature (°C.)                     -58                        -59                           -48                              -38                                 -35                                    -39                                       -36                                          -14    ML.sub.1+4 (100° C.)                     48 51 50 51 49 50 51 48    __________________________________________________________________________

Examples 1-10, Comparative Examples 1-6

In Table 2 are shown silane coupling agents used in these examples.

                  TABLE 2    ______________________________________    Compound    name          Structural formula    ______________________________________    Silane bis(3-     [(C.sub.2 H.sub.5 O).sub.3 SiC.sub.3 H.sub.6 ].sub.2                      S.sub.4    coupling           triethoxysilyl-    agent-1           propyl)           tetrasulfide    Silane coupling agent-2           trimethoxy- silylpropyl- benzothiazole tetrasulfide                       ##STR2##    ______________________________________

Rubber compositions were prepared by using the copolymer of Table 1 andthe silane coupling agent of Table 2 according to a compounding recipeshown in Table 3 (parts by weight). In Table 3, the amount of each ofthe copolymers used was 100 parts by weight. In these rubbercompositions, compounding chemicals other than copolymer, filler andsilane coupling agent were the same in Examples 1-10 and ComparativeExamples 1-6 and were shown by "note" in Table 3. With respect to theserubber compositions, the fracture strength (Tb), Lambourn abrasion indexand tan δ were measured to obtain results as shown in Table 3. Then,each of these rubber compositions was used to form a tread of a tirehaving a tire size of 165 SR 13, and thereafter the wet-skid resistance,rolling resistance and wear resistance were measured to obtain resultsas shown in Table 3.

                                      TABLE 3(a)    __________________________________________________________________________                   Compar-                         Compar-                               Compar-                   ative ative ative                   Example 1                         Example 2                               Example 3                                     Example 1                                           Example 2                                                 Example 3                                                       Example                                                             Example    __________________________________________________________________________                                                             5    Copolymer No.  4     1     2     3     4     5     6     7    Carbon black HAF                   50    10    10    10    10    10    10    10    Nipsil VN.sub.3                   --    40    40    40    40    40    40    40    Silane coupling agent-1                   --    3.0   0.3   3.0   3.0   3.0   3.0   3.0    Silane coupling agent-2                   --    --    --    --    --    --    --    --    Fracture strength (kg/cm.sup.2)                   242   221   235   241   251   253   257   255    Lambourn abrasion index                   100   85    90    101   107   111   118   115    tan δ (0° C.)                   0.343 0.285 0.271 0.321 0.353 0.361 0.363 0.346    tan δ (60° C.)                   0.135 0.075 0.078 0.075 0.076 0.077 0.078 0.085    Wet-skid resistance (index)                   100   91    90    101   105   104   105   104    Rolling resistance (index)                   100   123   122   122   123   122   121   115    Wear resistance (index)                   100   92    95    102   104   108   112   109    __________________________________________________________________________

                                      TABLE 3(b)    __________________________________________________________________________                                                 Compar-                                                       Compar-                                                             Compar-                                                 ative ative ative                   Example 6                         Example 7                               Example 8                                     Example 9                                           Example 10                                                 Example 4                                                       Example                                                             Example    __________________________________________________________________________                                                             6    Copolymer No.  8     4     6     4     6     4     4     4    Carbon black HAF                   10    10    10    25    25    45    10    10    Nipsil VN.sub.3                   40    40    40    35    35    5     40    40    Silane coupling agent-1                   3.0   --    --    1.0   1.0   3.0   0.1   12.0    Silane coupling agent-2                   --    3.0   3.0   --    --    --    --    --    Fracture strength (kg/cm.sup.2)                   252   249   257   250   255   239   198   178    Lambourn abrasion index                   113   106   117   105   109   97    79    72    tan δ (0° C.)                   0.521 0.361 0.351 0.342 0.353 0.331 0.362 0.310    tan δ (60° C.)                   0.090 0.076 0.077 0.079 0.080 0.127 0.131 0.081    Wet-skid resistance (index)                   107   105   104   103   104   99    104   97    Rolling resistance (index)                   110   121   122   120   120   101   101   115    Wear resistance (index)                   107   103   111   106   112   99    78    77    __________________________________________________________________________     Note) Compounding chemicals other than copolymer, filler and silane     coupling agent (parts by weight): aromatic oil 10, stearic acid 2,     Nphenyl-N'-isopropyl-p-phenylene diamine 1, zinc white 3,     Noxydiethylene-2-benzothiazole sulfenamide 0.6, di2-benzothiazylsulfide     0.8, sulfur 1.5.

As seen from Table 3, the pneumatic tires according to the invention areexcellent in all of the wet-skid resistance, rolling resistance and wearresistance.

Examples 11-14, Comparative Examples 7-9

Rubber compositions were prepared according to a compounding recipeshown in Table 4. Then, the same tests as in Example 1 were made withrespect to these rubber compositions as well as pneumatic tires madetherefrom to obtain results as shown in Table 4.

                                      TABLE 4    __________________________________________________________________________                         Compar-                               Compar-                                     Compar-                         ative ative ative                         Example 7                               Example 8                                     Example 9                                           Example 11                                                 Example 12                                                       Example                                                             Example    __________________________________________________________________________                                                             14    Natural rubber       --    80    80    70    70    30    30    Copolymer No. 4      100   20    20    30    --    70    --    Copolymer No. 6      --    --    --    --    30    --    70    Carbon black HAF     50    10    10    10    10    10    10    Nipsil VN.sub.3      --    40    40    40    40    40    40    Silane coupling agent-1                         --    3.0   3.0   3.0   3.0   3.0   3.0    Aromatic oil         10    10    10    10    10    10    10    Stearic acid         2.0   2.0   2.0   2.0   2.0   2.0   2.0    Zinc white           3.0   3.0   3.0   3.0   3.0   3.0   3.0    N-oxydiethylene-2-benzothiazole                         0.6   0.6   0.6   0.6   0.6   0.6   0.6    sulfeneamide    di-2-benzothiazyl sulfide (DM)                         0.8   0.8   0.8   0.8   0.8   0.8   0.8    N-phenyl-N'-isopropyl-p-phenylene diamine                         1.0   1.0   1.0   1.0   1.0   1.0   1.0    Sulfur               1.5   1.5   1.5   1.5   1.5   1.5   1.5    Fracture strength (kg/cm.sup.2)                         242   256   258   255   252   251   254    Lambourn abrasion index                         100   94    98    103   102   104   108    tan δ  (0° C.)                         0.343 0.279 0.280 0.320 0.317 0.347 0.350    tan δ (60° C.)                         0.135 0.075 0.074 0.076 0.075 0.077 0.078    Wet-skid resistance (index)                         100   89    89    101   102   102   105    Rolling resistance (index)                         100   124   125   121   123   122   121    Wear resistance (index)                         100   96    99    101   103   105   108    __________________________________________________________________________

Production Example 2

An autoclave of 5 l capacity provided with a stirrer and a jacket wasdried and purged with nitrogen. Into this autoclave were charged 2500 gof cyclohexane, 100 g of styrene, 400 g of 1,3-butadiene and 25 g oftetrahydrofuran. After the temperature inside the autoclave was renderedinto 10° C., the flow of cooling water was stopped and 0.300 g ofn-butyllithium was added with stirring at 2 rpm to conductpolymerization for 30 minutes. A part of the resulting polymer solutionwas taken out and then the Mooney viscosity thereof was measured to benot more than 14.

Thereafter, the remaining polymer solution was added with 9.38 m of asolution of monomethyltriphenoxy silane in cyclohexane (concentration:0.50 mol/l, mol ratio of monomethyltriphenoxy silane to n-butyllithiumof 1.0), whereby the yellowish red of the living anion disappeared andthe viscosity of the solution was raised. The reaction was furthercontinued at 50° C. for 30 minutes.

Then, 0.7 g of 2,6-di-t-butyl phenol (BHT) was added to 100 g of theresulting polymer, which was subjected to steaming to remove the solventand dried through hot rolls of 100° C. The yield of the polymer(copolymer No. 9) was substantially quantitative.

The copolymer Nos. 10-14 were prepared by the same method as describedabove except that various modifying agents shown in Table 5 were usedinstead of monomethyltriphenoxy silane. The copolymer No. 15 wasprepared by the same method as in the copolymer No. 9 except that themodifying agent was not used.

In Table 5 are shown the content of bound styrene, vinyl content inbutadiene portion, glass transition temperature and Mooney viscosity ofthe resulting copolymers.

                                      TABLE 5    __________________________________________________________________________    Copolymer No.            9      10   11    12     13       14   15    __________________________________________________________________________    ST (wt %) *1            25     25   25    25     25        5   25    Vi (%) *2            50     50   50    50     50       60   50    Coupling            monomethyl-                   tetra-                        dichloro-                              monochloro-                                     monochloro-                                              tetra-                                                   not used    agent   triphenoxy                   phenoxy                        diphenoxy                              triethoxy                                     methyldiphenoxy                                              phenoxy            silane silane                        silane                              silane silane   silane    ML.sub.1+4, 100° C.            50     51   48    48     51       51   50    Tg (°C.) *3            -38    -37  -38   -38    -36      -58  -39    __________________________________________________________________________     *1: content of bound styrene     *2: vinyl content in butadiene portion     *3: glass transition temperature

Examples 16-24, Comparative Examples 10-16

In these examples were used the same silane coupling agents as shown inTable 2.

Rubber compositions were prepared by using the copolymer of Table 5 andthe silane coupling agent according to a compounding recipe shown inTable 6 (parts by weight). In these rubber compositions, compoundingchemicals other than copolymer, filler and silane coupling agent werethe same in Examples 16-24 and Comparative Examples 10-16 and were shownby "note" in Table 6. With respect to these rubber compositions, thefracture strength (Tb), Lambourn abrasion index and tan δ were measuredto obtain results as shown in Table 6. Then, each of these rubbercompositions was used to form a tread of a tire having a tire size of165 SR 13, and thereafter the wet-skid resistance, rolling resistanceand wear resistance were measured to obtain results as shown in Table 6.

                                      TABLE 6(a)    __________________________________________________________________________                   Compar-                             Compar-                                                             Compar-                   ative                               ative ative                   Example 10                         Example 16                               Example 17                                     Example 18                                           Example 19                                                 Example 20                                                       Example                                                             Example    __________________________________________________________________________                                                             12    Copolymer No. 9      80    Copolymer No. 10           80    Copolymer No. 11                 80    Copolymer No. 12                       80    Copolymer No. 13                             80    Copolymer No. 14                                   80    Copolymer No. 15                                         80    NR             20    20    20    20    20    20    20    20    Carbon black HAF                   50    10    10    10    10    10    10    10    Silica filler VN.sub.3                   0     40    40    40    40    40    40    40    Silane coupling agent-1                   none  3     3     3     3     3     3     3    Silane coupling agent-2                   none    Fracture strength (kg/cm.sup.2)                   252   275   276   269   253   252   249   248    Lambourn abrasion index                   100   117   119   115   105   103   88    80    tan δ (0° C.)                   0.324 0.331 0.332 0.330 0.328 0.325 0.265 0.330    tan δ (60° C.)                   0.126 0.070 0.071 0.073 0.080 0.076 0.072 0.081    Wet-skid resistance (index)                   100   110   109   108   106   108   85    101    Rolling resistance (index)                   100   131   132   129   115   123   130   115    Wear resistance (index)                   100   115   117   112   105   105   95    85    __________________________________________________________________________

                                      TABLE 6(b)    __________________________________________________________________________                                           Compar-                                                 Compar-                                                       Compar-                                                             Compar-                                           ative ative ative ative                   Example 21                         Example 22                               Example 23                                     Example 24                                           Example 13                                                 Example 14                                                       Example                                                             Example    __________________________________________________________________________                                                             16    Copolymer No. 9                   80          80          80    5     80    80    Copolymer No. 10    Copolymer No. 11    Copolymer No. 12    Copolymer No. 13     80          80    Copolymer No. 14    Copolymer No. 15                   75    NR             20    20    20    20    20    20    20    20    Carbon black HAF                   10    10    25    25    10    10    45    10    Silica filler VN.sub.3                   40    40    35    35    40    40    5     40    Silane coupling agent-1    1.0   1.0   0.1   3.0   3.0   12.0    Silane coupling agent-2                   3     3    Fracture strength (kg/cm.sup.2)                   269   265   280   281   249   253   254   166    Lambourn abrasion index                   121   119   119   117   90    72    99    55    tan δ (0° C.)                   0.332 0.330 0.325 0.330 0.325 0.321 0.325 0.310    tan δ (60° C.)                   0.073 0.074 0.075 0.076 0.085 0.085 0.121 0.121    Wet-skid resistance (index)                   109   108   106   105   108   107   98    101    Rolling resistance (index)                   129   128   129   128   111   116   99    99    Wear resistance (index)                   113   111   116   115   94    86    99    65    __________________________________________________________________________     Note) Compounding chemicals other than copolymer, filler and silane     coupling agent (parts by weight): aromatic oil 10, stearic acid 2,     Nphenyl-N'-isopropyl-p-phenylene diamine 1, zinc white 3,     Noxydiethylene-2-benzothiazole sulfenamide 0.6, di2-benzothiazylsulfide     0.8, sulfur 1.5.

As mentioned above, in the pneumatic tires according to the invention,the rubber composition comprising polybutadiene or butadiene-styrenecopolymer or silane-modified polymer having a glass transitiontemperature of not lower than -50° C., silica filler and silane couplingagent within particular compounding ratio range is used as a treadrubber, so that the wet-skid resistance, rolling resistance and wearresistance are simultaneously satisfied.

What is claimed is:
 1. A pneumatic tire comprising a tread made from arubber composition comprising 10-150 parts by weight of a silica filler,not more than 150 parts by weight of carbon black, wherein said carbonblack and silica filler are present in a weight ratio of 95/5-10/90, and0.2-10 parts by weight of at least one silane coupling agent representedby the following general formula:

    Y.sub.3 --Si--C.sub.n H.sub.2n A                           (I)

(wherein Y is an alkyl group or alkoxyl group having a carbon number of1-4 or a chlorine atom, provided that the three Y's are the same ordifferent, n is an integer of 1-6, and A is an --S_(m) C_(n) H_(2n)Si--Y₃ group, an --X group or an S_(m) Z group (in which X is a nitrosogroup, a mercapto group, an amino group, an epoxy group, a vinyl group,an imido group or a chlorine atom, Z is a: ##STR3## group, each of m andn is an integer of 1-6 and Y is the same as mentioned above)), based on100 parts by weight of a polymer or copolymer rubber having a glasstransition temperature of not lower than -50° C. obtained bypolymerization of 1,3-butadiene or copolymerization of 1,3-butadiene andstyrene in an inert organic solvent with an organic alkali metalinitiator, or a rubber blend of not less than 30 parts by weight of theabove polymer or copolymer and not more than 70 parts by weight ofanother diene series rubber.
 2. The pneumatic tire according to claim 1,wherein said copolymer has a content of bound styrene of 15-50% byweight.
 3. The pneumatic tire according to claim 1, wherein the amountof single chain styrene introduced into the copolymer is less than 40%by weight of the total bound styrene content and the amount of longchain styrene having 8 or more styrene units is not less than 10% byweight of the total bound styrene content.
 4. The pneumatic tireaccording to claim 1, wherein said rubber composition contains 15-100parts by weight of said silica filler and 0.5-5 parts by weight of saidsilane coupling agent.
 5. The pneumatic tire according to claim 1,wherein said another diene series rubber is selected from the groupconsisting of natural rubber, cis-1,4-polyisoprene, emulsion-polymerizedstyrene-butadienecopolymer, solution-polymerizedstyrene-butadienecopolymer, low cis-1,4-polybutadiene, high cis-1,4-polybutadiene,ethylene-propylene-diene terpolymer, chloroprene, halogenated butylrubber and butadiene-acrylonitrile copolymer rubber.